What is delirium?

Delirium (new mental confusion) is a sudden change in mental status, or sudden confusion, that develops over hours to days. It is different from dementia, such as Alzheimer's disease, which is a chronic (long-term) state of confusion that develops and increases over time.

There are two types of delirium: hyperactive delirium and hypoactive delirium. Hyperactive means overactive (agitation, restlessness), while hypoactive means underactive (sleepy and hard to respond). Sometimes both types can occur together.

What causes delirium?

Some of the things that may cause delirium are:

  • Drugs.
  • Changes in the environment.
  • Lack of sleep.
  • Hormonal issues such as hyper-/hypo-thyroidism.
  • Lack of oxygen to the tissues.
  • Infections such as pneumonia or sepsis (an overwhelming reaction to infection).
  • Kidney or liver injury/failure.
  • Alcohol or illegal drug toxicity/overdose.
  • Pain.
  • Dehydration.  

What are the symptoms of delirium?

The symptoms of hyperactive delirium include:

  • Anxiety.
  • Restlessness.
  • Rapid changes in emotion.
  • Hallucinations.

The symptoms of hypoactive delirium include:

  • Flat affect.
  • Withdrawal.
  • Apathy.
  • Laziness.
  • Decreased responsiveness.


Last reviewed by a Cleveland Clinic medical professional on 11/09/2016.


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